How to make foam / bubbles in liquid
It looks like this would be possible to do with Boolean modifiers. Just create a sphere, deform it with modifiers so it looks more like a blob, then repeat it in a bubbly pattern within the fluid object. Once you've got all the bubbles where you want them, select them all and join them with CTRL + J. Then select the fluid, go to modifiers and add a Boolean modifier. Then select the bubbles under object. and apply.